http://msdn.microsoft.com/en-us/devlabs/ee794896.aspx

 

About Rx

Rx is a library for composing asynchronous and event-based programs using observable collections.

The “A” in “AJAX” stand for asynchronous, and indeed modern Web-based and Cloud-based applications are fundamentally asynchronous. In fact, Silverlight bans all blocking networking and threading operations. Asynchronous programming in by no means restricted to Web and Cloud scenarios, however. Traditional desktop applications also have to maintain responsiveness in the face of long latency IO operations and other expensive background tasks.

Another common attribute of interactive applications, whether Web/Cloud or client-based, is that they are event-driven. The user interacts with the application via a GUI that receives event streams asynchronously from the mouse, keyboard, and other inputs.

Rx is a superset of the standard LINQ sequence operators that exposes asynchronous and event-based computations as push-based, observable  collections via the new .NET 4.0 interfaces IObservable<T> and IObserver<T>.  These are the mathematical dual of the familiar IEnumerable<T> and IEnumerator<T> interfaces for pull-based, enumerable collections in the .NET framework.

The IEnumerable<T> and IEnumerator<T> interfaces allow developers to create reusable abstractions to consume and transform values from a wide range of concrete enumerable collections such as arrays, lists, database tables, and XML documents. Similarly, Rx allows programmers to glue together complex event processing and asynchronous computations using LINQ queries over observable collections such as .NET events and APM-based computations, PFx concurrent Task<T>,  the Windows 7 Sensor and Location APIs, SQL StreamInsight temporal event streams , F# first-class events, and async workflows.

Play with Rx, stress it, evaluate it, and tell us what you think.

….but F# removes side-effect corruption so uh.. there goes my analogy……

Starting from scratch with F#? Click here.

Functional programming is so addictive. It reminds me when I could code with no team, no deadline, no broken processes or cultures to navigate. I do hope this becomes a common option for general development or at least C# continues to borg functional ideas…

For a larger collection of F# samples, see:

http://go.microsoft.com/fwlink/?LinkID=124614

// F# Tutorial File
//
// This file contains sample code to guide you through the
// primitives of the F# language.
//
// Contents:
//   – Simple computations
//   – Functions on integers
//   – Tuples
//   – Booleans
//   – Strings
//   – Lists
//   – Arrays
//   – More Collections
//   – Functions
//   – Types: unions
//   – Types: records
//   – Types: classes
//   – Types: interfaces
//   – Types: classes with interface implementations
//   – Printing

// Turn on the lightweight syntax
#light

// open some standard namespaces
openSystem

// Simple computations
// —————————————————————
// Here are some simple computations.  Note how code can be documented
// with ‘///’ comments.  Hover over any reference to a variable to
// see its documentation.

/// A very simple constant integer
letint1 = 1

/// A second very simple constant integer
letint2 = 2

/// Add two integers
letint3 = int1 + int2

// Functions on integers
// —————————————————————

/// A function on integers
letf x = 2*x*x – 5*x + 3

/// The result of a simple computation
letresult = f (int3 + 4)

/// Another function on integers
letincrement x = x + 1

/// Compute the factorial of an integer
let rec factorial n =ifn=0then1elsen * factorial (n-1)

/// Compute the highest-common-factor of two integers
let rec hcf a b = // notice: 2 parameters separated by spaces
ifa=0thenb
elif a<bthenhcf a (b-a) // notice: 2 arguments separated by spaces
elsehcf (a-b) b
// note: function arguments are usually space separated
// note: ‘let rec’ defines a recursive function
// Tuples
// —————————————————————

// A simple tuple of integers
letpointA = (1, 2, 3)

// A simple tuple of an integer, a string and a double-precision floating point number
letdataB = (1,“fred”, 3.1415)

/// A function that swaps the order of two values in a tuple
letSwap (a, b) = (b, a)

// Booleans
// —————————————————————

/// A simple boolean value
letboolean1 =true

/// A second simple boolean value
letboolean2 =false

/// Compute a new boolean using ands, ors, and nots
letboolean3 = not boolean1 && (boolean2 ||false)

// Strings
// —————————————————————

/// A simple string
letstringA  =“Hello”

/// A second simple string
letstringB  =“world”

/// “Hello world” computed using string concatentation
letstringC  = stringA +” “+ stringB

/// “Hello world” computed using a .NET library function
letstringD = String.Join(” “,[| stringA; stringB |])
// Try re-typing the above line to see intellisense in action
// Note, ctrl-J on (partial) identifiers re-activates it

// Functional Lists
// —————————————————————

/// The empty list
letlistA = [ ]

/// A list with 3 integers
letlistB = [ 1; 2; 3 ]

/// A list with 3 integers, note :: is the ‘cons’ operation
letlistC = 1 :: [2; 3]

/// Compute the sum of a list of integers using a recursive function
let rec SumList xs =
matchxs with
| [] ->0
| y::ys ->y + SumList ys

/// Sum of a list
letlistD = SumList [1; 2; 3]

/// The list of integers between 1 and 10 inclusive
letoneToTen = [1..10]

/// The squares of the first 10 integers
letsquaresOfOneToTen = [forxin0..10->x*x ]

// Mutable Arrays
// —————————————————————

/// Create an array
letarr = Array.create 4“hello”
arr.[1] <-“world”
arr.[3] <-“don”

/// Compute the length of the array by using an instance method on the array object
letarrLength = arr.Length

// Extract a sub-array using slicing notation
letfront = arr.[0..2]

// More Collections
// —————————————————————

/// A dictionary with integer keys and string values
letlookupTable = dict [ (1,"One"); (2,"Two") ]

letoneString = lookupTable.[1]

// For some other common data structures, see:
//   System.Collections.Generic
//   Microsoft.FSharp.Collections
//   Microsoft.FSharp.Collections.Seq
//   Microsoft.FSharp.Collections.Set
//   Microsoft.FSharp.Collections.Map

// Functions
// —————————————————————

/// A function that squares its input
letSquare x = x*x

// Map a function across a list of values
letsquares1 = List.map Square [1; 2; 3; 4]
letsquares2 = List.map (funx->x*x) [1; 2; 3; 4]

// Pipelines
letsquares3 = [1; 2; 3; 4] |> List.map (funx->x*x)
letSumOfSquaresUpTo n =
[1..n]
|> List.map Square
|> List.sum

// Types: unions
// —————————————————————

typeExpr =
| Numofint
| AddofExpr * Expr
| Mul ofExpr * Expr
| Varofstring

let rec Evaluate (env:Map<string,int>) exp =
matchexpwith
| Num n->n
| Add (x,y)->Evaluate env x + Evaluate env y
| Mul (x,y)->Evaluate env x * Evaluate env y
| Var id ->env.[id]

letenvA = Map.of_list ["a",1 ;
"b",2 ;
"c",3 ]

letexpT1 = Add(Var“a”,Mul(Num 2,Var“b”))
letresT1 = Evaluate envA expT1

// Types: records
// —————————————————————

typeCard = { Name  : string;
Phone : string;
Ok    : bool }

letcardA = { Name =“Alf”; Phone =“(206) 555-8257″; Ok =false}
letcardB = { cardA withPhone =“(206) 555-4112″; Ok =true}
letShowCard c =
c.Name +” Phone: “+ c.Phone + (ifnot c.Okthen ” (unchecked)” else “”)

// Types: classes
// —————————————————————

/// A 2-dimensional vector
typeVector2D(dx:float, dy:float) =
// The pre-computed length of the vector
letlength = sqrt(dx*dx + dy*dy)
/// The displacement along the X-axis
memberv.DX = dx
/// The displacement along the Y-axis
memberv.DY = dy
/// The length of the vector
memberv.Length = length
// Re-scale the vector by a constant
memberv.Scale(k) = Vector2D(k*dx, k*dy)

// Types: interfaces
// —————————————————————

typeIPeekPoke =
abstractPeek: unit->int
abstractPoke: int->unit
// Types: classes with interface implementations
// —————————————————————

/// A widget which counts the number of times it is poked
typeWidget(initialState:int) =
/// The internal state of the Widget
let mutablestate = initialState

// Implement the IPeekPoke interface
interfaceIPeekPoke with
memberx.Poke(n) = state <- state + n
memberx.Peek() = state

/// Has the Widget been poked?
memberx.HasBeenPoked = (state <> 0)

letwidget = Widget(12) :> IPeekPoke

widget.Poke(4)
letpeekResult = widget.Peek()
// Printing
// —————————————————————

// Print an integer
printfn “peekResult = %d”peekResult

// Print a result using %A for generic printing
printfn “listC = %A”listC

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